Friends and family of the former N.F.L. player Joe McKnight gathered at the site of his fatal shooting in Terrytown, La., on Thursday.CreditMichael Democker/NOLA.com The Times-Picayune, via Associated Press

The man held in the fatal shooting of the former N.F.L. player Joe McKnight in Louisiana admitted to investigators that he had pulled the trigger, the authorities said, but he was allowed to walk free without charges on Friday while they investigated the case.

The man, Ronald Gasser, 54, was released overnight, hours after Mr. McKnight was shot three times about 2:45 p.m. Thursday in an apparent “road rage” episode in Terrytown, La., about five miles southeast of New Orleans, the sheriff’s office said.

In a statement, the Jefferson Parish Sheriff’s Office said that the two men had had a “heated verbal exchange.” During a news conference, Newell Normand, the sheriff, said the case might have escalated into violence because someone “recklessly” cut off the other while driving on a bridge.

The decision to release Mr. Gasser, who is white, infuriated supporters and former teammates of Mr. McKnight, who was black, and they took to social media to express outrage.

Sheriff Normand, appearing at times defiant and frustrated before reporters in Harvey, La., on Friday, said that the authorities would be very deliberate in the investigation, that witnesses were still being located and interviewed, and that people planning to protest must do it within a designated area or they would be jailed.

“This investigation is not going to be moved, influenced, coerced or changed in any way by any external force, comments or otherwise,” he said. “I can’t control what’s on the social networks, and if we want to continue to be silly, that’s fine.”

Asked if the case would be investigated as a hate crime, Sheriff Normand said that there was no evidence yet to suggest that it should be. “Everybody wants to make this about race,” he said. “This isn’t about race.”

Asked why Mr. Gasser was freed if he had admitted to the shooting, he said that in Louisiana there were some “relative statutes that provide defenses to certain crimes” and that the authorities would need to determine whether the shooting was justified.

He said that a man who had raised Mr. McKnight used to work as a deputy in the sheriff’s office and that some employees were “close with his family.” It was not immediately clear to whom he was referring; a 2007 profile in The Los Angeles Times said McKnight was raised by his mother, Jennifer McKnight.

Sheriff Normand disputed several rumors that had spread on social media, including that Mr. Gasser had stood over Mr. McKnight as he fired the gun, that a video has been recovered and that a witness had said Mr. McKnight apologized to Mr. Gasser before the shooting.

All of those are false, he said, and he advised people to believe only what they heard from officials like himself and the district attorney. “I strongly suggest you stop believing what you’re reading,” he said.

Councilman Mark Spears, who also spoke at the news conference, said: “It shouldn’t be a rush to judgment. The facts are still coming out, and we should base it on facts, not on Facebook and other social media.” He also said officials were “praying” for the McKnight family.

In a statement released before the news conference, the sheriff’s office said that Mr. Gasser had handed over a semiautomatic handgun to officers at the scene. The sheriff said at the news conference that Mr. Gasser had fired three rounds from inside his vehicle.

At a news conference, local N.A.A.C.P. officials criticized the authorities for releasing Mr. Gasser, pledging to demonstrate peacefully.

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Joe McKnight in 2013.CreditNFLPV, via Associated Press

“We think a black man was lynched yesterday,” said Morris Reed, the president of the New Orleans branch of the N.A.A.C.P. “We are demanding some answers.”

Moe Reed Jr., a lawyer, added, “There is nothing that could’ve happened yesterday at 3 p.m. in broad daylight on a Louisiana highway, in front of many people passing back and forth in front of a gas station, that would make this man feel that he was in danger of losing his life.”

Mr. McKnight’s family is also seeking answers, his grandmother Barbara Franklin told The Associated Press on Friday. She said she had learned of Mr. Gasser’s release through the radio. “He might be released now, but God is going to bring about justice,” she said.

Mr. McKnight, a running back and special teams standout, was a decorated player at the University of Southern California. He was picked in the fourth round of the N.F.L. draft by the New York Jets, where he played from 2010 to 2012 before being cut by the team in 2013.

He played two more N.F.L. games with the Kansas City Chiefs in 2014. In February, he joined the Canadian Football League, spending time with the Edmonton Eskimos and the Saskatchewan Roughriders.

Mr. Gasser is the owner of a telecommunications firm and a real estate business, according to The New Orleans Advocate.

The sheriff’s office on Friday night released details of a previous assault charge against Mr. Gasser stemming from an episode that happened at the same intersection as the shooting on Thursday.

It happened on Feb. 20, 2006, after a 51-year-old man called 911 to report that the driver of a red pickup truck was driving unsafely. The man saw a phone number on the truck to call if it was being operated unsafely and when he called the number, Mr. Gasser said he was the one driving.

The sheriff’s office said a “verbal altercation” began between the two and the man went to a service station at Holmes Boulevard and Berhman Highway in Terrytown to refuel his vehicle. Mr. Gasser, who had followed him, “confronted him and began to strike him with a closed fist several times,” the office said in a statement. Mr. Gasser drove away and the man called 911.

Investigators at a later date found Mr. Gasser and he was issued a misdemeanor summons for simple battery, which was dismissed, the office said. “We will continue to research this matter in order to determine the reason for the dismissal,” the statement said.

On Friday some social media users and McKnight’s former Jets teammates expressed bafflement and anger after Mr. Gasser was released.

“You’ve got to be kidding me,” Damon Harrison, a former Jet who currently plays for the New York Giants, wrote on Twitter. “Shoot in the air and you’re in jail for at least a week. Lord help us all.”

Damien Woody, a former offensive lineman and current N.F.L. analyst for ESPN, also said he had trouble understanding the move.

I try to be measured in these situations but how in the hell, less than 24 hours after the fact, u just let a man free who killed someone?!

In some ways, the episode bore close resemblance to the death of another pro athlete in New Orleans. In April, Will Smith, a former defensive end for the New Orleans Saints who was black, was shot and killed after a vehicle collision. In that case, Cardell Hayes, who is black, was arrested at the scene and charged with second-degree murder.

Jarvis DeBerry, a columnist for The Times-Picayune, wrote on Friday that the immediate response was noticeably different.

“Normand is going to have a tough time convincing the public that this isn’t another example of disparate responses to identical situations, another example of the race of the suspect altering the response to the crime,” he wrote.

A version of this article appears in print on , on Page D2 of the New York edition with the headline: Man Admitted Shooting Ex-Jet, Police Say, but Is Freed Without Charges. Order Reprints | Today’s Paper | Subscribe